Ultralight aircraft



FIG. 1 is a front perspective view of a ultralight aircraft showing my new design;

FIG. 2 is a side elevation view thereof, the opposite side being a mirror image of that shown;

FIG. 3 is a front elevation view thereof; and

FIG. 4 is a top plan view thereof. 

The ornamental design for a ultralight aircraft, substantially as shown and described. 